Purpose: To assess the performance of a Dual-Energy chest radiography system. Methods: A cohort of 129 patients was recruited from population referred for CT guided biopsy of a lung lesion. Digital radiography (DR) and Dual Energy (DE) images were acquired. Receiver operating characteristic (ROC) tests were performed to evaluate performance of DE images compared to DR. Five chest radiologists scored images. Performance was analyzed for all cases pooled and sub groups based on gender, nodule size, density, location, and chest diameter. Results: There was no significant difference between DE and DR for all cases (p = 0.61). There was a significant advantage for DE imaging of small nodules, and nodules located in right-upper lobe. (p = 0.02 and 0.01) Conclusions: DE imaging demonstrated significant improvement in diagnosis of sub-centimeter lung nodules and lesions in the upper lung zones which are common characteristic of early stage lung malignancy.

Purpose: To assess the performance of a Dual-Energy chest radiography system. Methods: A cohort of 129 patients was recruited from population referred for CT guided biopsy of a lung lesion. Digital radiography (DR) and Dual Energy (DE) images were acquired. Receiver operating characteristic (ROC) tests were performed to evaluate performance of DE images compared to DR. Five chest radiologists scored images. Performance was analyzed for all cases pooled and sub groups based on gender, nodule size, density, location, and chest diameter. Results: There was no significant difference between DE and DR for all cases (p = 0.61). There was a significant advantage for DE imaging of small nodules, and nodules located in right-upper lobe. (p = 0.02 and 0.01) Conclusions: DE imaging demonstrated significant improvement in diagnosis of sub-centimeter lung nodules and lesions in the upper lung zones which are common characteristic of early stage lung malignancy.

The purpose of this project was to explore the performance of methods for estimating stopping power ratio (SPR) from Hounsfield units (HU) using dual energy CT scans, rather than the standard single energy CT scans, with the aim of finding a method which could outperform the current single energy stoichiometric method. Such a method could reduce the margin currently added to the target volume during treatment which is defined as 3.5 % of the range to the target volume + 1 mm . Three such methods, by Taasti, Zhu, and, Lalonde and Bouchard, were chosen and implemented in MATLAB. A phantom containing 10 tissue-like inserts was scanned and used as a basis for the SPR estimation. To investigate the variation of the SPR from day-to-day the phantom was scanned once a day for 12 days. The resulting SPR of all methods, including the stoichiometric method, were compared with theoretical SPR values which were calculated using known elemental weight fractions of the inserts and mean excitation energies from the National Institute of Standards and Technology (NIST). It was found that the best performing method was the Taasti method which had, at best, an average percentage difference from the theoretical values of only 2.5 %. The Zhu method had, at best, 4.8 % and Lalonde-Bouchard 15.6% including bone tissue or 6.3 % excluding bone. The best average percentage difference of the stoichiometric method was 3.1 %. As the Taasti method was the best performing method and shows much promise, future work should focus on further improving its performance by testing more scanning protocols and kernels to find the ones yielding the best performance. This should then be supplemented with testing different pairs of energies for the dual energy scans. The fact that the Zhu and Lalonde-Bouchard method performed poorly could indicate problems with the implementation of those methods in this project. Investigating and solving those problems is also an important goal for future projects. Lastly the Lalonde-Bouchard method should be tested with more than two energy spectra.

PhD, Faculty of Engineering and the Built Environment, University of the Witwatersrand, 2010 / Dual Energy X-Ray Transmission (DE-XRT) Imaging is a multi-sensor technique employed to conduct particle-by-particle sorting. The system makes use of a dual energy x-ray line scan sensor, which generates images of the transmitted x-rays, similar to images generated for suitcase inspection in airport security applications. The dual energy x-ray system allows for rapid approximation of atomic number range, which is utilised to evaluate the mineral and maceral content of a variety of minerals, including coal. The process is independent of particle surface condition, and can thus be utilised as a dry process. A unique application of this technology is in the removal of torbanite from a coal deposit located in Mpumalanga, South Africa. The separation of coal from torbanite has been a problem for the coal industry for a long time. The separation of coal and torbanite by conventional gravity separation techniques is difficult, due to the overlapping densities of torbanite and coal. The commercial value of both commodities is significantly compromised if contaminated with the other, thus impacting negatively on the financial viability of mining such a deposit. Preliminary laboratory DE-XRT testwork results on high quality coal and torbanite products were promising. In order to evaluate the separation of typical Run of Mine (ROM) material on pilot scale, a production scale Mikrosort X-Tract Sorter was purchased. This was the first DE-XRT sorter available in South Africa, and was housed at Mintek in Johannesburg. A 150t sample was provided from a box cut adjacent to the coal deposit under investigation in order to conduct bulk and pilot sorting tests, the focus of which was on obtaining coal products of low ash and torbanite content. Clear distinctions between the coal, torbanite and shale fractions were observed using this technique. The sorter feed (-80mm+20mm) could be upgraded from a CV of 22MJ/kg to 28MJ/kg. Ash content could be reduced from 26% to 10%, which meets export quality standards. Petrographic analysis of the coal product indicated that a high purity coal product (in terms of torbanite and ash content) was attainable (91% by volume) at a mass yield of 42.9% to the coal product, with shale and mixed humic/sapropelic coal as contaminants. Under these conditions, torbanite contamination was marginal. It was demonstrated that shale could be removed from the torbanite product via a second sorting stage. This however was not the primary focus of the study, and was not optimised for this investigation. Two major limitations of the sorting process were identified, viz.; poor liberation and limited sorter feed size range. These impacted on the process as follows:- • The effects of poor liberation on coal quality could be counteracted by adjusting the sorting criteria of the algorithm to reject additional material. This would result in a lower coal product mass yield. In addition, interlocked coal/shale particles would report to the torbanite fraction. • A significant proportion of the ROM feed reported to the -20mm size fraction, and therefore did not fall part of the sorter feed. This resulted in a very low coal mass yield as a proportion of the ROM feed. If this process were to be adopted, means of minimizing fines production during mining and crushing would need to be investigated to improve overall yield to coal product. The capability to process coarse materials (-80mm+20mm) allows for throughputs in excess of 40t/hr. Consequently, this technique may be applied in simpler coal upgrading processes, such as coal deshaling in arid regions.

Mounting evidence suggests that the superposition of anatomical clutter in x-ray chest radiography poses a major impediment to the detectability of subtle lung nodules. Through decomposition of projections acquired using different x-ray energy spectra, dual-energy (DE) imaging offers to dramatically improve lung nodule conspicuity. The development of a high-performance DE chest imaging system is reported, with design and implementation guided by fundamental imaging performance metrics. Analytical and experimental studies of imaging performance guided the optimization of key acquisition technique parameters, including x-ray filtration, allocation of dose between low- and high-energy projections, and peak-kilovoltage selection. To minimize anatomical misregistration between images, a cardiac gating system was designed and implemented to direct x-ray exposures to within the quiescent period of the heart cycle. The instrumentation and optimal imaging techniques have been incorporated in a DE imaging prototype system now deployed in a clinical study to evaluate the diagnostic performance of DE imaging.

Dual Energy Computed Tomography (DECT) is an emerging technique that offers new possibilities to determine composition of tissues in clinical applications. Accurate knowledge of tissue composition is important for instance for brachytherapy (BT) treatment planning. However, the accuracy of CT numbers measured with contemporary clinical CT scanners is relatively low since CT numbers are affected by image artifacts. The aim of this work was to estimate the accuracy of CT numbers measured with the Siemens SOMATOM Definition Flash DECT scanner and the accuracy of the resulting volume or mass fractions calculated via the three material decomposition method. CT numbers of water, gelatin and a 3rd component (salt, hydroxyapatite or protein powder) mixtures were measured using Siemens SOMATOM Definition Flash DECT scanner. The accuracy of CT numbers was determined by (i) a comparison with theoretical (true) values and (ii) using different measurement conditions (configurations) and assessing the resulting variations in CT numbers. The accuracy of mass fractions determined via the three material decomposition method was estimated by a comparison with mass fractions measured with calibrated scales. The latter method was assumed to provide highly accurate results. It was found that (i) axial scanning biased CT numbers for some detector rows. (ii) large volume of air surrounding the measured region shifted CT numbers compared to a configuration where the region was surrounded by water. (iii) highly attenuating object shifted CT numbers of surrounding voxels. (iv) some image kernels caused overshooting and undershooting of CT numbers close to edges. The three material decomposition method produced mass fractions differing from true values by 8% and 15% for the salt and hydroxyapatite mixtures respectively. In this case, the analyzed CT numbers were averaged over a volumetric region. For individual voxels, the volume fractions were affected by statistical noise. The method failed when statistical noise was high or CT numbers of the decomposition triplet were similar. Contemporary clinical DECT scanners produced image artifacts that strongly affected the accuracy of the three material decomposition method; the Siemens’ image reconstruction algorithm is not well suited for quantitative CT. The three material decomposition method worked relatively well for averages of CT numbers taken from volumetric regions as these averages lowered statistical noise in the analyzed data.

Mounting evidence suggests that the superposition of anatomical clutter in x-ray chest radiography poses a major impediment to the detectability of subtle lung nodules. Through decomposition of projections acquired using different x-ray energy spectra, dual-energy (DE) imaging offers to dramatically improve lung nodule conspicuity. The development of a high-performance DE chest imaging system is reported, with design and implementation guided by fundamental imaging performance metrics. Analytical and experimental studies of imaging performance guided the optimization of key acquisition technique parameters, including x-ray filtration, allocation of dose between low- and high-energy projections, and peak-kilovoltage selection. To minimize anatomical misregistration between images, a cardiac gating system was designed and implemented to direct x-ray exposures to within the quiescent period of the heart cycle. The instrumentation and optimal imaging techniques have been incorporated in a DE imaging prototype system now deployed in a clinical study to evaluate the diagnostic performance of DE imaging.

Dual energy imaging has made it possible to enhance contrast in medical images using images containing different energy information, by combining low and high energy images. Dual energy data can either be acquired using double exposures or splitting the energy spectrum into two images using one exposure. This thesis presents investigations of dual energy imaging using a detector solution developed by XCounter which provides dual energy images in a single exposure with a threshold separating low and high energy images. Phantom experiments with phantoms of aluminum and plexiglas were performed using weighted logarithmic subtraction and basis material decomposition to produce dual energy images. Methods were validated and images were evaluated in terms of signal difference in noise ratio to find the threshold and tube voltage combination for optimum energy spectrum separation. The methods were also tested on biological materials using bone, soft tissue and iodine solution as contrast enhancer, to investigate K-edge imaging.  Optimal separation of plexiglas and aluminum were found at 70 kVp and the threshold parameter set within a range of 8 to 9, which corresponds to approximately 30 to 34 keV. For K-edge imaging, the optimum separation were found close to K-edge energy of iodine. The results found in the phantom study correlated with results from the biological material study.

Dual-energy (DE) x-ray imaging of the chest decomposes two radiographs acquired at low- and high x-ray energies into 'soft-tissue' and 'bone' images, reducing the influence of background anatomical noise and providing increased conspicuity of subtle underlying structures compared to conventional radiography. This thesis derives a quantitative theoretical model of imaging performance in DE x-ray imaging and employs the resulting framework to system optimization in thoracic imaging. Fourier domain metrics of signal and noise performance - including the noise-power spectrum (NPS), modulation transfer function (MTF), detective quantum efficiency (DQE), and noise-equivalent quanta (NEQ) - were computed using cascaded systems analysis extended to DE imaging and combined with a quantitative model of imaging task to yield estimates of detectability across a broad range of DE image acquisition and decomposition techniques. Specifically, the detectability index provided an objective function for optimizing the selection of kVp pair, added filtration, allocation of dose between low- and high- energy views, and choice of decomposition algorithm and parameters therein. Theoretical calculations were validated in comparison to measurements of NPS, MTF, DQE, and NEQ performed on an experimental DE imaging system and through human observer studies for a variety of imaging tasks. Overall, the detectability index was found to provide a reliable predictor of human observer performance. Results identified optimal DE image acquisition and decomposition techniques that boost detectability beyond that achieved by conventional radiography or other DE imaging approaches, in many cases boosting conspicuity of subtle lesions from barely visible to highly conspicuous at fixed dose to the patient. The results are particularly encouraging, as such performance was achieved with the DE imaging dose equivalent to that of a single chest radiograph. The theoretical framework provided a valuable guide to optimization of a clinical prototype for high-performance DE chest imaging and may be extended to other DE imaging approaches, such as DE mammography and DE computed tomography.

Dual-energy (DE) x-ray imaging of the chest decomposes two radiographs acquired at low- and high x-ray energies into 'soft-tissue' and 'bone' images, reducing the influence of background anatomical noise and providing increased conspicuity of subtle underlying structures compared to conventional radiography. This thesis derives a quantitative theoretical model of imaging performance in DE x-ray imaging and employs the resulting framework to system optimization in thoracic imaging. Fourier domain metrics of signal and noise performance - including the noise-power spectrum (NPS), modulation transfer function (MTF), detective quantum efficiency (DQE), and noise-equivalent quanta (NEQ) - were computed using cascaded systems analysis extended to DE imaging and combined with a quantitative model of imaging task to yield estimates of detectability across a broad range of DE image acquisition and decomposition techniques. Specifically, the detectability index provided an objective function for optimizing the selection of kVp pair, added filtration, allocation of dose between low- and high- energy views, and choice of decomposition algorithm and parameters therein. Theoretical calculations were validated in comparison to measurements of NPS, MTF, DQE, and NEQ performed on an experimental DE imaging system and through human observer studies for a variety of imaging tasks. Overall, the detectability index was found to provide a reliable predictor of human observer performance. Results identified optimal DE image acquisition and decomposition techniques that boost detectability beyond that achieved by conventional radiography or other DE imaging approaches, in many cases boosting conspicuity of subtle lesions from barely visible to highly conspicuous at fixed dose to the patient. The results are particularly encouraging, as such performance was achieved with the DE imaging dose equivalent to that of a single chest radiograph. The theoretical framework provided a valuable guide to optimization of a clinical prototype for high-performance DE chest imaging and may be extended to other DE imaging approaches, such as DE mammography and DE computed tomography.